1. Field of the Invention
The present invention generally relates to a liquid crystal on silicon (LCoS) cell structure. In particular, the present invention relates to a liquid crystal on silicon cell structure with a composite post spacer which surrounds to form a cell space.
2. Description of the Prior Art
In modern planar display technology, plasma display panels (PDPs) and liquid crystal displays (LCDs) are popular choices. They both constitute numerous display grids called pixel cells. The former one is applied in a large-sized market and still has not reached widespread acceptance since the technique for mass production has still not been perfected and because cost is still high. A thin-film transistor LCD (TFT LCD), which has prevailed in recent years, is representative of the latter one.
A liquid crystal on silicon (LCoS) display is a display which utilizes a silicon chip as a substrate and utilizes a standard CMOS process to form pixel cell matrices, integrated drivers, and other electronic devices on the silicon chip. An advantage of the LCOS display is its utilization of the CMOS process, since the CMOS process is well developed in the present semiconductor industry. As a result, high stability and reliability can be achieved when compared to the LCD. In addition, using this process, each pixel pitch can be shrunk to less than 10 μm, therefore high resolutions are obtained.
Moreover, a liquid crystal on silicon display also has the advantages of having small pixel sizes, high brightness, high resolution, simple fabricating processes, low cost, and a small volume. Therefore the liquid crystal on silicon display panels have been applied to video and media equipments, such as handy cameras, digital cameras, projection TVs, and multi-media overhead projectors.
The liquid-crystal-on-silicon projection systems work on similar principles to LCD projection systems. A significant difference between a liquid crystal on silicon display projection system and an LCD projection system is the way to modulate light within the projection system. The LCD projection system has a transmissive architecture, and light emitted from a light source has to pass liquid crystal so as to be modulated. The liquid crystal on silicon display projection system has a reflective architecture and uses a liquid crystal on silicon display panel, which is composed of a glass substrate, liquid crystal, and a CMOS chip with electricity circuits and a reflective layer coated thereon, to modulate optical signals produced by a light source and reflect the modulated signals to a projection screen.
The difference between an LCOS display and a conventional thin film transistor-liquid crystal display (TFT-LCD) is materials used for forming substrates. Both a cover substrate and a backplane are made of glass in a TFT-LCD. Nevertheless, the cover substrate in an LCOS display is made of glass, but the backplane in an LCOS display is a semiconductor silicon substrate. Therefore, an LCOS process combines LCD techniques and complementary metal-oxide semiconductor (CMOS) processes.
When compared to the PDP, the LCOS display not only has an absolute superiority in cost but also has intrinsic advantages of the LCD. In addition, being assisted with adequate projection techniques, the liquid crystal on silicon display can further be applied in markets for large-sized displays. Therefore, the liquid crystal on silicon display attracts many major manufacturers to devote themselves to development, and is the display with the highest potential.
Traditionally speaking, a sealant is used in a liquid crystal on silicon display panel. Please refer to FIG. 1, illustrating a conventional liquid crystal on silicon display panel. The liquid crystal on silicon display panel 1 includes a silicon substrate (a lower substrate) 10 and a glass substrate (an upper substrate) 20. There is a sealant 30 sandwiched between the lower substrate 10 and the upper substrate 20. The sealant 30 on one hand may glue the lower substrate 10 firmly to the upper substrate 20. The sealant 30 on the other hand may keep the lower substrate 10 and the upper substrate 20 apart a suitable distance so that a liquid crystal 40 may fill the chamber, called a cell space 41, which is surrounded by the lower substrate 10, the upper substrate 20 and the sealant 30. Also, pixel electrodes 50 are arranged in an array on the lower substrate 10 within the sealant 30.
However, due to the technical and market demands on the liquid crystal on silicon display panels, the distance between the lower substrate 10 and the upper substrate 20 is getting shorter and shorter, and the sealant 30 is accordingly getting harder and harder to use to define the thickness of the cell space 41, called a cell gap. In addition, because the sealant 30 is translucent, light within the cell space 41 may escape and the contrast of the liquid crystal on silicon display panel 1 as a result deteriorates.
Currently, spacer balls are used to replace the sealant 30 for defining the thickness of the cell space 41. However, in one aspect it is an easy task to fabricate spacer balls of uniform size, and in another aspect the process also gets more complicated to add the spacer balls into the liquid crystal on silicon display panel 1.
As a result, a novel liquid crystal on silicon cell structure is still needed. The novel liquid crystal on silicon cell structure should be able to maintain the thickness of the cell spacer in the absence of space balls. Moreover, the novel liquid crystal on silicon cell structure should also be able to maintain the thickness of the cell spacer to be as small as possible.